The present embodiment relates generally to a composition for sealing a subterranean zone penetrated by a wellbore and, more particularly, to methods and compositions for sealing an expandable tubular such as a pipe, pipe string, casing, liner or the like in a wellbore.
In the drilling and completion of an oil or gas well, a composition is often introduced in the wellbore for cementing casing or pipe strings. In this process, known as “primary cementing,” a composition is pumped into the annular space between the walls of the wellbore and the pipe string. The composition sets in the annular space, supporting and positioning the pipe string, and forming a substantially impermeable barrier which divides the wellbore into subterranean zones. After primary cementing, the undesirable migration of fluids between zones is prevented. Likewise, compositions are often subsequently introduced into a subterranean zone for remedial operations to recover circulation or to plug the wellbore. Most remedial operations comprise introducing a composition into the wellbore to reestablish a seal between the zones.
Previously, a variety of cement compositions have been used for cementing. However, cement is undesirable for use with expandable casing. After the expandable casing is placed down hole, a mandrel is run through the casing to expand the casing, and expansions up to twenty five percent are possible. As cement is incompressible, expansion of the casing can lead to crushing of the cement, and consequent loss of effectiveness regarding the zones. Therefore, a resilient sealing composition with comparable strength to cement, but greater elasticity and compressibility is required for cementing expandable casing.